Development of the Metal Rheology Model of High-temperature Deformation for Modeling by Finite Element Method

It is shown that when modeling the processes of forging and stamping, it is necessary to take into account not only the hardening of the material, but also softening, which occurs during hot processing. Otherwise, the power parameters of the deformation processes are precisely determined, which leads to the choice of more powerful equipment. Softening accounting (processes of stress relaxation) will allow to accurately determine the stress and strain state (SSS) of the workpiece, as well as the power parameters of the processes of deformation. This will expand the technological capabilities of these processes. Existing commercial software systems for modeling hot plastic deformations based on the finite element method (FEM) do not allow this. This is due to the absence in these software products of the communication model of the component deformation rates and stresses, which would take into account stress relaxation. As a result, on the basis of the Maxwell visco-elastic model, a relationship is established between deformation rates and stresses. The developed model allows to take into account the metal softening during a pause after hot deformation. The resulting mathematical model is tested by experiment on different steels at different temperatures of deformation. The process of steels softening is determined using plastometers. It is established experimentally that the model developed by 89 ... 93 % describes the rheology of the metal during hot deformation. The relationship between the components of the deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation. As a result, the number of iterations and calculations has significantly decreased

Improving the Quality of Forgings Based on Upsetting the Workpieces with Concave Facets

We propose a forging method for forgings, which implies the upsetting of workpieces with concave facets. A procedure for the theoretical research has been devised aimed at studying the mechanism of closure of artificial axial defects in workpieces. The study was performed based on a finite element method. The key examined parameter was the depth of the concave facets in a workpiece. This parameter varied in the range 0.75; 0.85; and 0.80. The angle of the concave facets was 120°. The results of the theoretical study are the following distributions: deformations, temperatures, and stresses in the body of a workpiece in the process of upsetting the workpieces with concave facets. Based on these parameters, we established an indicator of the stressed state in the axial zone of the workpiece.In order to verify the theoretical results obtained, a procedure for experimental research has been developed. The study was performed using the lead and steel workpieces. The results of the theoretical study allowed us to establish that the effective depth of the concave facets is the ratio of diameters of protrusions and ledges equal to 0.85. At this ratio there occurs the intensive closure of an axial defect. This is due to the high level of compressive stresses when upsetting the workpieces with concave facets. We have established the effective degree of deformation at which the intensive closure of defects takes place. Also established are the distributions of deformations for the cross-section and height of the workpiece, as well as a change in the indicator of the stressed state in the process of upsetting workpieces with concave facets. The closure of axial defects has been confirmed by experimental study using lead and steel samples.The new technique for upsetting workpieces with concave facets has been implemented. The results of ultrasonic testing have allowed us to establish that the obtained parts do not have internal defects, which exceed the requirements of the European standard SEP 1921. Our research has led to the conclusion of the high efficiency of the proposed new method for upsetting workpieces with concave facets, which implies the improvement of quality of the axial zone of large forgings when using a given technique

Modeling the Techological Process of Pipe Forging Without a Mandrel

A broaching technique for thick-walled pipes has been investigated. The proposed technique implies the deformation of a hollow workpiece without a mandrel. The procedure has been devised to conduct theoretical studies using FEM. The procedure is aimed at determining the thermal, stressed state and a shape change in the workpiece while forging pipes without the use of a mandrel. The variables applied were the internal diameter of a hollow workpiece, which ranged in the interval of 0.30; 0.55; 0.80. Based on the finite-element modeling, the following was established: the distribution of temperatures and intensity of logarithmic deformations within the volume of a pipe after broaching without the use of a mandrel. The diameter of a pipe's hole has been determined, which is formed at broaching when applying a given technique. The dependences of intensity of lengthening and thickening of the wall of a pipe have been established. A special indicator was devised to estimate the elongation rate of a pipe. It was determined that increasing the inner diameter increases the lengthening of a pipe and decreases the intensity of the hole forging. The common dependence for the simulated broaching schemes is that the magnitude of elongation of a hollow workpiece changes insignificantly for different degrees of reductions at constant relative sizes of a pipe. It has made it possible to establish a recommended feed in order to increase the elongation of a hollow forging and to decrease the degree of closing a hole. The rational feed shall be (0.05...0.15)D. The results from the finite element modeling were verified by experimental study using lead samples. An experimental modeling procedure has been devised. It was established that at an inside diameter of the workpiece of (0.5...0.6)D one observes a maximum of the wall thickening. It was established that the results for a workpiece shape change, obtained from a theoretical study using FEM, exceeded those acquired experimentally by 9.14 %. The validity of results from theoretical modelling is confirmed by data from experiments on decreasing the internal diameter of the pipe. Difference between the theoretical and experimental results amounts to 9...12 %. The established patterns make it possible to determine the resulting diameter of a pipe's hole. It was found based on the results from modeling that it is impossible to broach pipe workpieces without a mandrel. This technique extends the possibilities of technological processes aimed at manufacturing pipe workpieces

Investigating the Process of Shrinkage Depression Formation at the Combined Radial-backward Extrusion of Parts with a Flange

The possibilities of using an energy method to forecast defect formation in the form of shrinkage depression in the combined extrusion processes have been investigated. We have proposed a mathematical model of the combined radial-reverse extrusion process of hollow details with a flange, taking into consideration the degeneration of the trapezoidal module into a rectangular one. Separate stages in the deformation process have been defined, depending on the magnitude of the active tool stroke compared with the thickness of the bottom of the cup. We have devised a generalized estimation scheme for the process of combined radial-reverse extrusion of parts with a flange taking into consideration the final stage of deformation (Hbottom<h1). The magnitude of the reduced pressure of deformation has been derived as a function of the geometric, technological, and kinematic parameters of the extrusion process. A role of the kinematic parameter of the process belongs to a relative speed of metal flow in the vertical direction (filling the cup's wall at the inverse flow of metal). The magnitude for the reduced pressure of deformation has been optimized based on this parameter. We have analyzed the character of change in the optimum magnitude of a relative speed of metal flow in the vertical direction in the course of the process. The differences have been established in the derived dependences of a given kinematic parameter for the process with the formation of shrinkage depression in the bottom part of a component and without defect formation.It has been substantiated that the use of combined extrusion in the manufacture of hollow parts with a flange, when compared with the application of simple schemes of deformation, improves the technological capabilities of the process. We have proven that the technologies for introducing combined extrusion had not been sufficiently studied and there is a lack of recommendations on predicting the formation of a defect in the form of shrinkage depression. The estimation scheme has been proposed for the radial-reverse extrusion process, taking into consideration the emergence of shrinkage depression at the final stage of deformation. We have modeled the process of combined extrusion of hollow parts with a flange and established the influence of friction conditions on the time of the emergence of shrinkage depression in the bottom part of a component.It has been confirmed that the proposed generalized estimation scheme makes it possible to predicting the occurrence of a defect in the form of shrinkage depression at all stages and under different technological conditions for a deformation process. Obtaining a preliminary assessment, based on it, of possible defect formation would facilitate the development of appropriate technological recommendations to avoid defects of this typ

Effect of the Tool Geometry on the Force Mode of the Combined Radial-direct Extrusion with Compression

A possibility has been investigated to use an energy method to calculate the energy-force parameters for the cold extrusion processes involving components of complex configuration. A mathematical model has been proposed for the process of combined sequential radial-direct extrusion with compression with the presence of triangular kinematic modules. The use of the triangular kinematic modules with curvilinear and straight-line boundaries has made it possible to describe the sites of intense deformation, which correspond to the steady stage of the deformation process. It has been proposed to apply an upper estimate of the power of forces that deform a kinematic module of the triangular shape of the transition zone from the radial flow of metal to direct extrusion. This has made it possible to derive the magnitude of the reduced deformation pressure in the analytical form as a function of the geometric and technological parameters of the extrusion process. The margin of error, compared to numerical calculations without the use of the upper estimate, does not exceed 0.2‒1 %. The role of an optimization parameter belongs to aÎ(0,1), which is responsible for the shape of the curvilinear boundary of the inner triangular kinematic module. We have derived an analytical expression for the optimal value of the α parameter and analyzed a change in the magnitude of the reduced deformation pressure at different ratios of the process geometric parameters. It has been established that the optimal values of the angle of inclination of the forming mandrel β lie between 20° and 30° for different ratios of the deformation process.It has been justified that the use of combined sequential extrusion in the manufacture of hollow components with a flange, when compared to the application of simple deformation schemes, improves the process technological possibilities. The lack of study of the schemes of the combined radial-direct extrusion process with the compression of components of the type of sleeve, as well as the lack of recommendations for calculating the energy force parameters of the process, have been confirmed. The calculation scheme of a given process, developed on the basis of an energy method, makes it possible to predict the force mode for the steady stage under different technological parameters of the deformation process. The data acquired on the estimation of the optimal parameters for tool configuration would help devise appropriate design and technology recommendation

Designing A Kinematic Module with Rounding to Model the Processes of Combined Radial-longitudinal Extrusion Involving A Tool Whose Configuration is Complex

It is advisable that parts whose shape is complex and which are made from solid or hollow blanks should be made by means of transverse and combined radial-longitudinal extrusion. The variation of manufacturing modes, tool configurations (in the form of chambers and rounding of the transitional sections of matrices) requires an adequate preliminary assessment of the force regime and the features of part shape formation. This paper has proposed a curvilinear kinematic module of the trapezoidal form for modeling radial-longitudinal extrusion processes in the presence of matrix rounding. Given the impossibility of using a quarter-circle boundary for the kinematically assigned possible velocity field, it has been proposed to use approximate curves in the form of z1(r) and z2(r). Taking into account the slightest deviation in the length of the arc of the approximate curve z1(r) and the area of the curvilinear trapezoid bounded by it relative to a quarter of the circle (not exceeding 0.8 % for any ratio), it has been recommended using this particular replacement. We have performed calculations of the value of the reduced deformation pressure inside the kinematic module with rounding taking into consideration the power of cutting forces at the border with adjacent kinematic modules. As an example, the devised module with rounding embedded in the estimation scheme of radial extrusion was analyzed. A significant impact of friction conditions on the force mode and the corresponding optimal value of the rounding radius have been identified. The resulting kinematic module makes it possible to expand the capabilities of the energy method for modeling cold extrusion processes involving the tools of complex form according to new deformation schemes. That could contribute to preparing recommendations on the optimal tool configuration and more active industrial implementation of these processe

Predicting the Shape Formation of Parts with A Flange and an Axial Protrusion in the Process of Combined Aligned Radial-direct Extrusion

Using the calculation schemes CS-1 (with the presence of a trapezoid module) and CS-1a (with rectangular kinematic modules) has been proposed for the process of the combined radial-direct extrusion of parts with a flange and an axial protrusion. The application of a trapezoidal kinematic module allows the description of the characteristic regions of metal flow, close to the actual course of the process based on the distorted coordinate grids. On the basis of the energy method, the values of the reduced deformation pressure have been obtained using the upper estimate of the power of deformation forces inside the trapezoidal kinematic module. The optimization involved the parameter Rk that determines the position of the surface of the interface of metal flow into an axial protrusion and a flange zone. We have performed a comparative analysis of the theoretical calculations of the magnitude of the reduced deformation pressure and the influence of geometric ratios and friction conditions on the qualitative and quantitative differences in the character of the change in the resulting curves. The overestimation of data on assessing the force mode based on the CS-1a scheme relative to the calculations based on the CS-1 scheme can be as high as 50 % and indicates the rationality of using the latter. This is due to the limitation in the use of the optimization (the absence of the optimization of the height of the deformation site) for the scheme containing elementary rectangular kinematic modules. The deviation from the experimentally obtained increments in an axial protrusion does not exceed 7‒10 %, which indicates the validity of the use of the CS-1 estimation scheme with a trapezoidal kinematic module. Thus, it can be argued that it is correct to determine the position of the boundary of the surface of the interface of metal flow into an axial protrusion and a flange zone and the resulting assessment of the formation of a semi-finished produc

Predicting the Shape Formation of Hollow Parts with A Flange in the Process of Combined Radial-reverse Extrusion

The simulation of the process of combined radial reverse extrusion of hollow parts with a flange has established two fundamentally different, in terms of the components of the kinematic modules, calculation schemes CDZ-1.i and CDZ-2.j, taking into consideration the possible shape of the boundary of the section of a metal flow inside a workpiece. The comparison of the dependences of the optimal relative rate of metal outflow in the opposite direction for different schemes indicates significant differences in the resulting values in the course of the deformation process. The relevance of this study is due to making it easier to evaluate the use of the combined extrusion process to produce hollow parts with a flange while maintaining the required dimensions compared to simple deformation schemes. We have identified the lack of detailed studies into the technologies for the introduction of combined extrusion schemes, as well as the absence of technological recommendations for determining the force regime and the shape formation of a semi-finished article.The process of the combined extrusion of hollow parts with a flange was investigated, thereby selecting different types based on the nature of the metal flow depending on the geometric ratios of the deformation process. We have obtained experimental data on the gradual shape formation of a semi-finished product in the process of deformation at different geometric ratios. The limits of using estimation schemes of the process have been defined to obtain data on the increments in a semi-finished product, including in terms of predicting the formation of a shrinkage cavity in the bottom part. It is recommended that a condition of selecting the appropriate scheme should be the condition for a minimum value of the reduced pressure of deformation ̅pi< ̅pj. The resulting recommendations make it easier to predict the shape formation and the force mode of extrusion (a deviation from experimentally obtained data can be reduced to 10 %), which would contribute to evaluating the rationality of the combined extrusion processes while ensuring the required dimensions of a par

Determination of the Peculiarities of Obtaining Coatings of Different Hardness on Structural Steel at Diffusion Metalization

The features of obtaining coatings on carbon steel, structural steel St 3 are studied during diffusion metallization – simultaneous saturation of steel with boron, chromium and aluminum (boron chromium aluminizing), without the use of special heat treatment. The basic compositions of powder mixtures are established using the simplex lattice method, which make it possible to obtain boride structures of increased hardness, phases of a solid solution of boron, chromium and aluminum in Feα and the predicted depth of the surface layer on the surface of carbon steel. The characteristic features of the microhardness formation of the surface layer of coatings are established depending on the composition of the saturating mixture. An important factor is established for the effect of aluminum on the microhardness of the surface layer in multicomponent systems. Its presence contributes to the formation of solid solutions. New data are obtained on the formation of surface layers during steel saturation with boron, chromium and aluminum, and the conditions for obtaining layers of high hardness and high ductility are determined. The optimal areas for the formation of coatings of various structures and depths by the simplex planning method are found. As optimization factors, let's use the relative planes occupied by borides and solid solution, as well as the depth of the surface layers. It is clearly shown how the structure of surface layers changes depending on the quantitative relations between the components of saturating mixtures. The graphical dependences of the boride phase, the phase of the solid solution and the depth of the layer, on the composition of the saturating mixture during diffusion metallization (boron chromium aluminizing) allow to improve the process in order to obtain coatings with increased wear resistance on the surface of carbon stee